The present invention relates generally to band brakes and also to mechanisms having a rotating member adapted to be equipped with a brake of this kind.
Such mechanisms are in particular hydraulically operated clutches, especially multidisc clutches, which comprise two coaxial rotating parts, of which one will hereinbelow be referred to as the driven part, which forms a rotating member and comprises two elements which are in a cylinder-piston relationship to one another and which form between them a pressure chamber of variable volume, while the other part will hereinbelow be referred to as the driving part and comprises at least one friction disc which is intended to be axially gripped in engagement by the component elements of the aforesaid driven part in order to fasten the latter rotationally to the driving part when fluid under pressure is delivered into the pressure chamber, and which further comprise elastic means interposed between the component elements of the driven part and urge the latter into the disengaged position, releasing the friction disc.
Clutches of this kind are used in particular for serving a power take-off on tractors.
One of the problems which has to be solved in the construction of clutches of this kind results from the fact that the fluid used in particular for their lubrication and cooling, which in practice is oil, brings about, by a drag effect, undesirable rotation of the driven part when the latter is in the position of disengagement in relation to the driving part, which may make difficult the engagement of any rotary member which is to be operated on the power take-off controlled by the said driven part.
In order to obviate this difficulty it has already been proposed to provide for the driven part of such a clutch a brake adapted to be applied to the said driven part when the latter is in the position of disengagement relative to the corresponding driving part.
In order to take advantage of the presence of the fluid under pressure necessary for operating the clutch, it is usual for this same fluid to be used for operating the brake associated with the clutch.
Among arrangements of this type which are known at the present time it has been proposed to use a brake having a piston type hydraulically operating member adapted to apply a brake shoe against a cylindrical bearing surface on the driven part which is to be controlled.
In clutches of the kind in question it is usual for the clutch to be mounted on a support forming a bearing for its driven part.
This has the consequence that an axial offset inevitably exists between the bearing surface supporting this driven part, and the braking bearing surface of the driven part on which the brake associated with it has to act.
Because of this axial offset, when the brake associated with the driven part of the clutch is operated the driven part is subjected to a tilting moment relative to the support carrying it, and in practice this results in rapid wear of the support.
The present invention has in particular the aim of obviating this disadvantage and to this end proposes to use in a clutch of the kind in question a band brake adapted to apply an at least statically radially balanced action to the driven part of a clutch of this kind.
More precisely it has primarily as an object a band brake of this kind.
Band brakes are well known per se; they comprise a brake band wrapped in a loop around a cylindrical bearing surface of the rotating member which is to be braked, and of an operating member adapted to apply the said brake band against at least part of the cylindrical surface.
A brake of this kind is used in particular in the hydraulically operated multidisc clutch for direct and reverse running which is described in French Pat. No. 926,278.
However, in this patent the operating element used for controlling the brake, which is a hydraulically operated device, comprises only a single piston which is coupled to one end of the brake band in question, while the other end of the brake is coupled to the fixed casing of the whole arrangement.
This results on the one hand in the continued existence of a radial reaction resultant which is not zero, during braking, on the part in question of the clutch, and on the other hand in considerable complexity of the clutch.
The band brake according to the invention makes it possible to avoid these disadvantages and in addition offers other advantages.